The present invention relates to an apparatus for controlling tilt of an axle of industrial vehicles such as forklifts. More particularly, the present invention relates to an apparatus that locks a tiltable axle, which supports wheels, for prohibiting tilt of the axle as necessary. The present invention further relates to an apparatus and a method for estimating the location of the center of gravity in the fore-and-aft direction of an industrial vehicle.
In a typical industrial vehicle such as a forklift, the rear axle, which supports rear wheels, is pivotally secured to the body frame. The rear axle thus tilts with respect to the body frame thereby allowing all of the front and rear wheels to always contact the road surface even if the vehicle runs over bumps and dips. As a result, the vehicle travels in a stable manner. However, the tiltable rear axle causes the body frame to be inclined by centrifugal force when the vehicle is turning. In other words, the tiltable rear axle degrades the stability of the vehicle during turning of the vehicle.
Japanese Unexamined Patent Publication No. 58-211903 describes a forklift that has a mechanism for locking a tiltable axle against tilt. The mechanism locks the tiltable axle to the body frame when detected centrifugal force exceeds a predetermined value. Thus, when a great centrifugal force acts on the forklift, inclination of the body frame is restricted. This stabilizes steerage of the forklift.
Japanese Unexamined Patent Publication No. 58-167215 also describes a forklift that has a mechanism for locking a tiltable axle against tilt. This mechanism locks the tiltable axle to the body frame when the weight of a carried object is greater than or equal to a predetermined value and the position of the forks are higher or equal to a predetermined height. When the carried object is heavy and is elevated to a relatively high position, the center of gravity of the vehicle is at a higher location. The higher location of the center of gravity makes the forklift unstable. However, the locking mechanism locks the axle to the body frame thereby allowing the forklift to lift and lower the object and to turn in a stable manner.
However, when locked to the body frame, the axle does not tilt relative to the body frame in accordance with the condition of the road surface. This may result in one of the front and rear wheels separating from the road surface. When an object on the forks is light or when there is no object on the forks, the center of gravity is located relatively close to the rear end of the forklift. Therefore, locking the rear axle against tilt may cause one of the front wheels to separate from the road surface. When a relatively heavy object is mounted on the forks, the center of gravity is located relatively close to the front end of the forklift. In this state, locking the rear axle to the body frame may cause one of the rear wheels to separate from the road surface.
In a typical forklift, the front wheels are driven. Therefore, if one of the front wheels separates from the road surface or if the pressure pressing the front wheel against the road surface is decreased, the front wheel races. The racing of the front wheel prevents the driving force of the front wheels from being transmitted to the road surface. This hinders the traveling of the forklift.